Wavelength multiplexing device

ABSTRACT

A wavelength multiplexing device is disclosed. When light is irradiated on a first longitudinal end region of a metal nano-structure, surface plasmon polaritons are generated in the first longitudinal end region. The surface plasmon polaritons and the light are coupled with each other to form first coupled surface plasmon polaritons, wherein the first coupled surface plasmon polaritons propagate along and on a surface of the metal nano-structure. When the first coupled surface plasmon polaritons reach a two-dimensional material layer, excitons are induced in the two-dimensional material layer, wherein the induced excitons and the first coupled surface plasmon polaritons are coupled with each other to form second coupled surface plasmon polaritons. The second coupled surface plasmon polaritons propagate along and on a surface of the metal nano-structure toward a second longitudinal end thereof.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.15/455,492 filed Mar. 10, 2017, which claims the benefit under 35 U.S.C.119(a) of Korean Patent Application No. 10-2016-0029780 filed Mar. 11,2016, in the Korean Intellectual Property Office, the disclosures ofwhich are incorporated herein by reference for all purposes.

BACKGROUND Field of the Invention

The present disclosure relates to a wavelength multiplexing device, and,more particularly, to a wavelength multiplexing device using couplingbetween SPPs (surface plasmon polaritons) generated from a metalnano-structure and excitons induced in a transition metaldichalcogenide-based compound.

Discussion of Related Art

Photonics with light manipulation meet the latest information technologyneeds for high-speed data processing. Conventionally, quantum dots (QDs)or quantum wells (QWs) have been widely used in optical communication.In this connection, a top-down approach wherein quantum dots arearranged in a series of arrays, and a quantum well growth forthree-dimensional stacking are expensive and still need improvement.Further, short-life excitons have operational limits at lowtemperatures.

The wavelength conversion and multiplexing technique is intended fordesigning a reconfigurable optical communication system. Various methodsfor wavelength conversion have been developed in conventional opticalcommunication technologies based on optical fibers and opticalwaveguides. Further, miniaturization of optical components forapplication in nano-electronics has allowed new fusion ofoptoelectronics. However, optical diffraction limitation is afundamental obstacle with regards to reducing the size of opticaldevices to nanometers.

SUMMARY OF THE INVENTION

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify all key featuresor essential features of the claimed subject matter, nor is it intendedto be used alone as an aid in determining the scope of the claimedsubject matter.

Surface plasmon polaritons (SPPs), that is, couplings betweenelectromagnetic waves and electron plasma from a metal, have thepotential to overcome the above optical diffraction limitation. This isbecause the surface plasmon polaritons allow localization of the lightenergy and thus light-guidance in an area of a size smaller than awavelength of an interface between the metal and the dielectric.Therefore, the present disclosure is to provide a wavelengthmultiplexing device to overcome the optical diffraction limitation usingSSPs (surface plasmon polaritons).

In this connection, the present disclosure is to provide a wavelengthmultiplexing device using coupling between SPPs (surface plasmonpolaritons) generated from a metal nano-structure using a light sourceand excitons induced in a transition metal dichalcogenide-basedcompound.

In a first aspect of the present disclosure, there is provided awavelength multiplexing device comprising: a two-dimensional materiallayer made of a semiconductor material; an elongate metal nano-structurehaving first and second opposing longitudinal ends, wherein the firstlongitudinal end thereof is spaced from the two-dimensional materiallayer, and the elongate metal nano-structure is partially disposed onthe two-dimensional material layer; a light source configured toirradiate light onto the first longitudinal end region of the metalnano-structure, wherein when the light is irradiated on the firstlongitudinal end region of the metal nano-structure, surface plasmonpolaritons are generated in the first longitudinal end region, whereinthe surface plasmon polaritons and the light are coupled with each otherto form first coupled surface plasmon polaritons, wherein the firstcoupled surface plasmon polaritons propagate along and on a surface ofthe metal nano-structure, wherein when the first coupled surface plasmonpolaritons reach the two-dimensional material layer, excitons areinduced in the two-dimensional material layer, wherein the inducedexcitons and the first coupled surface plasmon polaritons are coupledwith each other to form second coupled surface plasmon polaritons,wherein the second coupled surface plasmon polaritons propagate alongand on a surface of the metal nano-structure toward the secondlongitudinal end thereof.

In one embodiment of the first aspect, the light has a first wavelength,wherein each of the excitons has a second wavelength different from thefirst wavelength.

In one embodiment of the first aspect, the second coupled surfaceplasmon polaritons are decoupled at the second longitudinal end of themetal nano-structure into first light with the first wavelength andsecond light with the second wavelength.

In one embodiment of the first aspect, the device further comprises asemiconductor substrate having an insulating film formed thereon,wherein the two-dimensional material layer is disposed on the insulatingfilm.

In one embodiment of the first aspect, the insulating film is made ofsilicon dioxide (SiO₂), and the semiconductor substrate is formed of asilicon (Si) wafer.

In one embodiment of the first aspect, a voltage is applied to thesubstrate.

In one embodiment of the first aspect, an amount of the induced excitonsis adjusted by the voltage applied to the substrate.

In one embodiment of the first aspect, the two-dimensional materiallayer is electrically grounded.

In one embodiment of the first aspect, the metal nano-structure includesa metal nano-wire.

In one embodiment of the first aspect, the two-dimensional materiallayer is in a form of a thin film having an atomic layer thickness.

In one embodiment of the first aspect, the semiconductor materialincludes at least one selected from a group consisting of a transitionmetal dichalcogenide-based compound, a chalcogenide-based semiconductorcompound, a phosphorus-containing chalcogenide-based semiconductorcompound, and a phosphorus-containing semiconductor compound.

In a second aspect of the present disclosure, there is provided awavelength multiplexing device comprising: a first material layer madeof a first semiconductor material; a second material layer made of asecond semiconductor material, wherein the first material layer isspaced from the second material layer; an elongate metal nano-structurehaving first and second opposing longitudinal ends, wherein the elongatemetal nano-structure extends across and on the first and second materiallayers; a light source configured to irradiate light onto a first regionof the metal nano-structure, wherein the first region overlaps the firstmaterial layer, wherein when the light is irradiated on the first regionof the metal nano-structure, surface plasmon polaritons are generated onthe first region of the metal nano-structure, and first excitons areinduced in the first material layer, wherein the surface plasmonpolaritons and the first excitons are coupled with each other to formfirst coupled surface plasmon polaritons, wherein the first coupledsurface plasmon polaritons propagate along and on a surface of the metalnano-structure, wherein when the first coupled surface plasmonpolaritons reach the second material layer, second excitons are inducedin the second material layer, wherein the second excitons and the firstcoupled surface plasmon polaritons are coupled with each other to formsecond coupled surface plasmon polaritons, wherein the second coupledsurface plasmon polaritons propagate along and on a surface of the metalnano-structure.

In one embodiment of the second aspect, each of the first excitons has afirst wavelength, wherein each of the second excitons has a secondwavelength different from the first wavelength.

In one embodiment of the second aspect, the second coupled surfaceplasmon polaritons are decoupled at one of the first and secondlongitudinal ends of the metal nano-structure into first light with thefirst wavelength and second light with the second wavelength.

In one embodiment of the second aspect, the device further comprises asemiconductor substrate having an insulating film formed thereon,wherein the first and second material layers are disposed on theinsulating film.

In one embodiment of the second aspect, a voltage is applied to thesubstrate.

In one embodiment of the second aspect, each of the first and secondlayers is electrically grounded.

In one embodiment of the second aspect, an amount of the induced firstand/or second excitons is adjusted by the voltage applied to thesubstrate.

In one embodiment of the second aspect, each of the first and secondmaterial layer is in a form of a thin film having an atomic layerthickness.

In one embodiment of the second aspect, each of the first and secondsemiconductor material includes at least one selected from a groupconsisting of a transition metal dichalcogenide-based compound, achalcogenide-based semiconductor compound, a phosphorus-containingchalcogenide-based semiconductor compound, and a phosphorus-containingsemiconductor compound.

In a third aspect of the present disclosure, there is provided awavelength multiplexing device comprising: a first material layer madeof a first semiconductor material; a second material layer made of asecond semiconductor material, wherein the second material layer isdisposed on the first material layer; an elongate metal nano-structurehaving first and second opposing longitudinal ends, wherein the elongatemetal nano-structure is partially disposed on the second material layer;a light source configured to irradiate light onto a first region of themetal nano-structure, wherein the first region overlaps the first andsecond material layers, wherein when the light is irradiated on thefirst region of the metal nano-structure, surface plasmon polaritons aregenerated on the first region of the metal nano-structure, firstexcitons are induced in the first material layer, and second excitonsare induced in the second material layer, wherein the surface plasmonpolaritons are coupled with the first and second excitons to form firstcoupled surface plasmon polaritons, wherein the first coupled surfaceplasmon polaritons propagate along and on a surface of the metalnano-structure.

In one embodiment of the third aspect, each of the first excitons has afirst wavelength, wherein each of the second excitons has a secondwavelength different from the first wavelength.

In one embodiment of the third aspect, the first coupled surface plasmonpolaritons are decoupled at one of the first and second longitudinalends of the metal nano-structure into first light with the firstwavelength and second light with the second wavelength.

In one embodiment of the third aspect, each of the first and secondmaterial layer is in a form of a thin film having an atomic layerthickness.

In one embodiment of the third aspect, each of the first and secondsemiconductor material includes at least one selected from a groupconsisting of a transition metal dichalcogenide-based compound, achalcogenide-based semiconductor compound, a phosphorus-containingchalcogenide-based semiconductor compound, and a phosphorus-containingsemiconductor compound.

In a fourth aspect of the present disclosure, there is provided awavelength multiplexing device comprising: a first material layer madeof a first semiconductor material; a second material layer made of asecond semiconductor material, wherein the first material layer isspaced from the second material layer; a third material layer made of athird semiconductor material, wherein the third material layer is spacedfrom the second material layer, and the second material layer isdisposed between the first and third material layers; an elongate metalnano-structure having first and second opposing longitudinal ends,wherein the elongate metal nano-structure extends across and on thefirst, second and third material layers; a light source configured toirradiate light onto a first region of the metal nano-structure, whereinthe first region overlaps the first material layer, wherein when thelight is irradiated on the first region of the metal nano-structure,surface plasmon polaritons are generated on the first region of themetal nano-structure, and first excitons are induced in the firstmaterial layer, wherein the surface plasmon polaritons and the firstexcitons are coupled with each other to form first coupled surfaceplasmon polaritons, wherein the first coupled surface plasmon polaritonspropagate along and on a surface of the metal nano-structure, whereinwhen the first coupled surface plasmon polaritons reach the secondmaterial layer, second excitons are induced in the second materiallayer, wherein the second excitons and the first coupled surface plasmonpolaritons are coupled with each other to form second coupled surfaceplasmon polaritons, wherein the second coupled surface plasmonpolaritons propagate along and on a surface of the metal nano-structure,wherein when the second coupled surface plasmon polaritons reach thethird material layer, third excitons are induced in the third materiallayer, wherein the third excitons and the second coupled surface plasmonpolaritons are coupled with each other to form third coupled surfaceplasmon polaritons, wherein the third coupled surface plasmon polaritonspropagate along and on a surface of the metal nano-structure.

In one embodiment of the fourth aspect, a voltage is applied to each ofthe first, second, and third material layers.

In one embodiment of the fourth aspect, each of the first excitons has afirst wavelength, wherein each of the second excitons has a secondwavelength different from the first wavelength, wherein each of thethird excitons has a third wavelength different from the first andsecond wavelengths.

In one embodiment of the fourth aspect, an amount of the induced first,second and/or third excitons is adjusted by the voltage.

In one embodiment of the fourth aspect, the metal nano-structure has aprotective coating formed on a surface thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and form a part ofthis specification and in which like numerals depict like elements,illustrate embodiments of the present disclosure and, together with thedescription, serve to explain the principles of the disclosure.

FIG. 1 is a conceptional view for illustrating a wavelength multiplexingdevice in accordance with one embodiment of the present disclosure.

FIG. 2A is a conceptional view for illustrating a wavelengthmultiplexing device in accordance with one embodiment of the presentdisclosure.

FIG. 2B shows a photoluminescence (PL) image for the wavelengthmultiplexing device in FIG. 2A and a graph of a photoluminescence signal(PL signal) based on a wavelength for the wavelength multiplexing devicein FIG. 2A.

FIG. 3A is a conceptional view for illustrating a wavelengthmultiplexing device in accordance with one embodiment of the presentdisclosure.

FIG. 3B shows a photoluminescence (PL) image for the wavelengthmultiplexing device in FIG. 3A and a graph of a photoluminescence signal(PL signal) based on a wavelength for the wavelength multiplexing devicein FIG. 3A.

FIG. 4 is a conceptional view for illustrating a wavelength multiplexingdevice in accordance with one embodiment of the present disclosure.

For simplicity and clarity of illustration, elements in the figures arenot necessarily drawn to scale. The same reference numbers in differentfigures denote the same or similar elements, and as such perform similarfunctionality. Also, descriptions and details of well-known steps andelements are omitted for simplicity of the description. Furthermore, inthe following detailed description of the present disclosure, numerousspecific details are set forth in order to provide a thoroughunderstanding of the present disclosure. However, it will be understoodthat the present disclosure may be practiced without these specificdetails. In other instances, well-known methods, procedures, components,and circuits have not been described in detail so as not tounnecessarily obscure aspects of the present disclosure.

DETAILED DESCRIPTION OF THE INVENTION

Examples of various embodiments are illustrated and described furtherbelow. It will be understood that the description herein is not intendedto limit the claims to the specific embodiments described. On thecontrary, it is intended to cover alternatives, modifications, andequivalents as may be included within the spirit and scope of thepresent disclosure as defined by the appended claims.

It will be understood that, although the terms “first”, “second”,“third”, and so on may be used herein to describe various elements,components, regions, layers and/or sections, these elements, components,regions, layers and/or sections should not be limited by these terms.These terms are used to distinguish one element, component, region,layer or section from another element, component, region, layer orsection. Thus, a first element, component, region, layer or sectiondescribed below could be termed a second element, component, region,layer or section, without departing from the spirit and scope of thepresent disclosure.

It will be understood that when an element or layer is referred to asbeing “connected to”, or “coupled to” another element or layer, it canbe directly on, connected to, or coupled to the other element or layer,or one or more intervening elements or layers may be present. Inaddition, it will also be understood that when an element or layer isreferred to as being “between” two elements or layers, it can be theonly element or layer between the two elements or layers, or one or moreintervening elements or layers may also be present.

Spatially relative terms, such as “beneath,” “below,” “lower,” “under,”“above,” “upper,” and the like, may be used herein for ease ofexplanation to describe one element or feature's relationship to anotherelement s or feature s as illustrated in the figures. It will beunderstood that the spatially relative terms are intended to encompassdifferent orientations of the device in use or in operation, in additionto the orientation depicted in the figures. For example, if the devicein the figures is turned over, elements described as “below” or“beneath” or “under” other elements or features would then be oriented“above” the other elements or features. Thus, the example terms “below”and “under” can encompass both an orientation of above and below. Thedevice may be otherwise oriented for example, rotated 90 degrees or atother orientations, and the spatially relative descriptors used hereinshould be interpreted accordingly.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the presentdisclosure. As used herein, the singular forms “a” and “an” are intendedto include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms“comprises”, “comprising”, “includes”, and “including” when used in thisspecification, specify the presence of the stated features, integers,operations, elements, and/or components, but do not preclude thepresence or addition of one or more other features, integers,operations, elements, components, and/or portions thereof. As usedherein, the term “and/or” includes any and all combinations of one ormore of the associated listed items. Expression such as “at least oneof” when preceding a list of elements may modify the entire list ofelements and may not modify the individual elements of the list.

Unless otherwise defined, all terms including technical and scientificterms used herein have the same meaning as commonly understood by one ofordinary skill in the art to which this inventive concept belongs. Itwill be further understood that terms, such as those defined in commonlyused dictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art andwill not be interpreted in an idealized or overly formal sense unlessexpressly so defined herein.

In the following description, numerous specific details are set forth inorder to provide a thorough understanding of the present disclosure. Thepresent disclosure may be practiced without some or all of thesespecific details. In other instances, well-known process structuresand/or processes have not been described in detail in order not tounnecessarily obscure the present disclosure.

As used herein, the term “substantially,” “about,” and similar terms areused as terms of approximation and not as terms of degree, and areintended to account for the inherent deviations in measured orcalculated values that would be recognized by those of ordinary skill inthe art. Further, the use of “may” when describing embodiments of thepresent disclosure refers to “one or more embodiments of the presentdisclosure.”

As used herein and used on many papers and articles, terms such assurface plasmas (SPs), surface plasma waves, surface electromagneticwaves, surface polaritons, surface plasmon polaritons (SPPs), plasmonsurface polaritons (PSPs) all may refer to electromagnetic waves excitedin the metal surface.

The plasmon phenomenon refers to a phenomenon in which the freeelectrons in a metal collectively resonate due to externalelectromagnetic field applied thereto, and, thus, an electromagneticfield around the metal is locally enhanced due to the oscillation.

FIG. 1 is a conceptional view for illustrating a wavelength multiplexingdevice in accordance with one embodiment of the present disclosure.Referring to FIG. 1, a wavelength multiplexing device 1000 may include ametal nano-structure 110, a light source 120, a two-dimensional materiallayer 130, an insulating film 140 and a semiconductor substrate 150.

In one example, the metal nano-structure 110 may be embodied as silver(Ag) nano-wires. However, the present disclosure is not limited thereto.Various metals may be employed for the nano-wires. In one example, themetal nano-structure 110 may be embodied as metal nano-rods.

The light source 120 may emit laser which may be incident on a firstlongitudinal end region of the metal nano-structure 110. A firstlongitudinal end of the metal nano-structure 110 may refer to one ofboth opposing longitudinal ends of the metal nano-structure 110. In thisconnection, the first longitudinal end region may refer to an areaadjacent to the first longitudinal end. The light from the light source120 may cause electron oscillation in the metal nano-structure 110 togenerate surface plasmon polaritons. When the light from the metalnano-structure 110 encounters the first longitudinal end region, thelight may be scattered there.

When the surface plasmon polaritons may be generated in the firstlongitudinal end region, the surface plasmon polaritons and the lightare coupled with each other to form first coupled surface plasmonpolaritons which, in turn, may propagate on and along the surface of themetal nano-structure 110.

The two-dimensional material layer 130 may be made of a semiconductormaterial in which excitons may be induced. The two-dimensional materiallayer 130 may be spaced from the first longitudinal end of the metalnano-structure 110. In one example, an insulating film 140 may be formedon a semiconductor substrate 150, and the two-dimensional material layer130 may be disposed on the insulating film 140. The metal nano-structure110 may be partially disposed on the two-dimensional material layer 130.In one example, the metal nano-structure 110 may partially extend acrossand on the two-dimensional material layer 130. The two-dimensionalmaterial layer 130 may be in the form of a thin film having an atomiclayer thickness. The semiconductor material may include at least oneselected from a group consisting of a transition metaldichalcogenide-based compound, a chalcogenide-based semiconductorcompound, a phosphorus-containing chalcogenide-based semiconductorcompound, and a phosphorus-containing semiconductor compound. Forexample, the two-dimensional material layer 130 may be made of, but maybe not limited to, tungsten disulfide (WS₂), tungsten diselenide (WSe₂),or molybdenum disulfide (MoS₂). The two-dimensional material layer 130may be electrically grounded, while a voltage may be applied to thesemiconductor substrate 150.

The first coupled surface plasmon polaritons propagating along and onthe surface of the metal nano-structure 110 may induce excitons in thetwo-dimensional material layer 130. Thus, the induced excitons and thefirst coupled surface plasmon polaritons may be coupled with each other.The amount of the induced excitons may be controlled by the voltage (Vg)applied to the semiconductor substrate 150. In this connection, when thevoltage (Vg) is applied to the semiconductor substrate 150, excesscarriers are doped into the two-dimensional material layer 130, and,thus, the amount of the induced excitons may be adjusted by the carrierdoping amount. The amount of the excitons for switching information canbe adjusted based on the electrical doping.

The light from the light source 120 may have a first wavelength λ₀ andthe induced exciton may have a second wavelength λ₁ different from thefirst wavelength λ₀. Those different wavelengths may be multiplexed viathe coupling process. In one example, the second wavelength may begreater than the first wavelength. The second wavelength λ₁ may bedetermined by the bandgap of the two-dimensional material layer 130.Therefore, it is possible to change the second wavelength λ₁ by changingthe kind of the transition metal dichalcogenide-based compound formingthe two-dimensional material layer 130.

The excitons and the first coupled surface plasmon polaritons may becoupled with each other to generate the second coupled surface plasmonpolaritons, which in turn, may propagate along the surface of the metalnano-structure 110. In this connection. The second coupled surfaceplasmon polaritons may propagate along the surface of the metalnano-structure 110 while different wavelengths thereof are multiplexed.Thus, the second coupled surface plasmon polaritons may be scattered onthe second longitudinal end of the metal nano-structure to be decoupledinto first light with the first wavelength and second light with thesecond wavelength. Thus, the second coupled surface plasmon polaritonsmay be de-multiplexed into the first light with the first wavelength andthe second light with the second wavelength. In this way, the firstlight with the first wavelength and second light with the secondwavelength may be collected individually. The collected first light withthe first wavelength and second light with the second wavelength may beemployed for corresponding communications.

FIG. 2A is a conceptional view for illustrating a wavelengthmultiplexing device in accordance with one embodiment of the presentdisclosure. FIG. 2B shows a photoluminescence (PL) image for thewavelength multiplexing device in FIG. 2A and a graph of aphotoluminescence signal (PL signal) based on a wavelength for thewavelength multiplexing device in FIG. 2A.

Referring to FIG. 2A, a wavelength multiplexing device 2000 may includea metal nano-structure 210, a light source 220, a first material layer230, a second material layer 240, an insulating film 250, and asemiconductor substrate 260.

Each of the first material layer 230 and second material layer 240 maybe made of a semiconductor material in which excitons may be inducedtherein. The first material layer 230 and second material layer 240 maybe spaced from each other. The semiconductor material may include atleast one selected from a group consisting of a transition metaldichalcogenide-based compound, a chalcogenide-based semiconductorcompound, a phosphorus-containing chalcogenide-based semiconductorcompound, and a phosphorus-containing semiconductor compound. Forexample, the first material layer 230 may be made of molybdenumdisulfide (MoS₂) while the second material layer 240 may be made oftungsten diselenide (WSe₂). However, the present disclosure may belimited thereto. Each of the first material layer 230 and secondmaterial layer 240 may be electrically grounded, while a voltage may beapplied to the semiconductor substrate 260. Each of the first materiallayer 230 and second material layer 240 may be in the form of a thinfilm having an atomic layer thickness.

The metal nano-structure 210 may be disposed on the first material layer230 and the second material layer 240. In one example, the metalnano-structure 210 may be embodied as silver (Ag) nano-wires. However,the present disclosure is not limited thereto. Various metals may beemployed for the nano-wires. In one example, the metal nano-structure210 may be embodied as metal nano-rods. The first material layer 230 andthe second material layer 240 may be disposed on the insulating film 250on the substrate 260. The metal nano-structure 210 may extend across thefirst material layer 230 and the second material layer 240. A voltagemay be applied to the semiconductor substrate 260. One or more of theamounts of first excitons and second excitons as will be described latermay be controlled by the voltage applied to the semiconductor substrate150.

The light source 220 may emit laser light with a wavelength λ₀ which inturn, may be incident on a first region of the metal nano-structure 210wherein the first region may overlap the first material layer 230. Thelaser light may induce the first excitons in the first material layer230 and may generate surface plasmon polaritons in the first region.Then, the first excitons and surface plasmon polaritons may be coupledwith each other in the first region to form first coupled surfaceplasmon polaritons which in turn, may propagate along the surface of themetal nano-structure 210.

Then, the first coupled surface plasmon polaritons may be absorbed bythe second material layer 240 and, thus, the second excitons may beinduced in the second material layer 240. Then, the second excitons andfirst coupled surface plasmon polaritons may be coupled with each otherto form second coupled surface plasmon polaritons which in turn, maypropagate along the surface of the metal nano-structure. In one example,each of the first excitons may have a first wavelength λ₁, while each ofthe second excitons may have a second wavelength λ₂ different from thefirst wavelength. In one example, the second wavelength may be largerthan the first wavelength.

The second coupled surface plasmon polaritons may propagate along thesurface of the metal nano-structure 210 while different wavelengthsthereof are multiplexed. Thus, the second coupled surface plasmonpolaritons may be scattered on a longitudinal end of the metalnano-structure 210 to be decoupled into first light with the firstwavelength and second light with the second wavelength. Thus, the secondcoupled surface plasmon polaritons may be demultiplexed into the firstlight with the first wavelength and the second light with the secondwavelength. In this way, the first light with the first wavelength andsecond light with the second wavelength may be collected individually.The collected first light with the first wavelength and second lightwith the second wavelength may be employed for correspondingcommunications.

Referring to FIG. 2B, the wavelength λ₀ may refer to a wavelength of thelaser from the light source 220. C₁ and C₂ may refer to concentrationsof the photoluminescence signal. The photoluminescence spectra(de-multiplexed) for the wavelength λ₁ of the first exciton induced inthe first material layer 230 made of molybdenum disulfide (MoS₂) and thewavelength λ₂ of the second exciton induced in the second material layer240 made of tungsten diselenide (WSe₂) respectively may be observed inthe C2 area (the longitudinal end of the elongate nano-structure 210).Thus, the multiplexed first and second excitons may be de-multiplexed inthe C2 area. In the C1 area, the first and second excitons may bemultiplexed with each other.

FIG. 3A is a conceptional view for illustrating a wavelengthmultiplexing device in accordance with one embodiment of the presentdisclosure. FIG. 3B shows a photoluminescence (PL) image for thewavelength multiplexing device in FIG. 3A and a graph of aphotoluminescence signal (PL signal) based on a wavelength for thewavelength multiplexing device in FIG. 3A.

Referring to FIG. 3A, a wavelength multiplexing device 3000 may includea metal nano-structure 310, a light source 320, a first material layer330, and a second material layer 340.

The first material layer 330 may be made of a first semiconductormaterial in which first excitons may be induced therein. The secondmaterial layer 340 may be made of a second semiconductor material inwhich second excitons may be induced therein. Each of the first materiallayer 330 and second material layer 340 may be in the form of a thinfilm having an atomic layer thickness. Each of the first material layer330 and second material layer 340 may include at least one selected froma group consisting of a transition metal dichalcogenide-based compound,a chalcogenide-based semiconductor compound, a phosphorus-containingchalcogenide-based semiconductor compound, and a phosphorus-containingsemiconductor compound. In one example, the first material layer 330 maybe made of tungsten disulfide (WS₂) while the second material layer 340may be made of tungsten diselenide (WSe₂). However, the presentdisclosure may be limited thereto. The first material layer 330 andsecond material layer 340 may be stacked on top of another. In oneexample, the second material layer 340 may be disposed on the firstmaterial layer 330 as shown in FIG. 3A.

The metal nano-structure 310 may be disposed on the second materiallayer 340. In one example, the metal nano-structure 310 may be embodiedas silver (Ag) nano-wires. However, the present disclosure is notlimited thereto. Various metals may be employed for the nano-wires. Inone example, the metal nano-structure 310 may be embodied as metalnano-rods. The elongate metal nano-structure 310 may extend across thesecond material layer 340.

The light source 320 may emit laser light with a wavelength λ₀ which inturn, may be incident on a first region of the metal nano-structure 310wherein the first region may overlap the first material layer 330 andsecond material layer 340. In one example, the wavelength λ₀ may be 514nm.

The laser light may induce first excitons in the first material layer330 and second excitons in the second material layer 340, and maygenerate surface plasmon polaritons in the first region. Then, the firstand second excitons may be coupled with the surface plasmon polaritonsin the first region to form first coupled surface plasmon polaritonswhich in turn, may propagate along the surface of the metalnano-structure 310.

In one example, each of the first excitons may have a first wavelengthλ₁, while each of the second excitons may have a second wavelength λ₂different from the first wavelength. In one example, the secondwavelength may be larger than the first wavelength.

The first coupled surface plasmon polaritons may propagate along thesurface of the metal nano-structure 310 while different wavelengthsthereof are multiplexed. Thus, the first coupled surface plasmonpolaritons may be scattered on a longitudinal end of the metalnano-structure 310 to be decoupled into first light with the firstwavelength and second light with the second wavelength. Thus, the firstcoupled surface plasmon polaritons may be demultiplexed into the firstlight with the first wavelength and the second light with the secondwavelength. In this way, the first light with the first wavelength andsecond light with the second wavelength may be collected individually.The collected first light with the first wavelength and second lightwith the second wavelength may be employed for correspondingcommunications.

In FIG. 3B, an upper image indicates a photoluminescence (PL) image forthe wavelength multiplexing device in FIG. 3A, while a lower graphindicates a graph of a photoluminescence signal (PL signal) based on awavelength for the wavelength multiplexing device in FIG. 3A. In thelower graph, a large graph c indicates a photoluminescence signal (PLsignal) based on the wavelength in the first region onto which the laseris incident, while a small graph d indicates a photoluminescence signal(PL signal) based on the wavelength in the second region as a rightlongitudinal end of the nano-structure 310.

Referring to FIG. 3B, the large graph c indicating a photoluminescencesignal (PL signal) based on the wavelength in the first region ontowhich the laser is incident may be identical with the small graph dindicating a photoluminescence signal (PL signal) based on thewavelength in the second region as a right longitudinal end of thenano-structure 310. In other words, a photoluminescence signal (PLsignal) based on the wavelength in the first region where the slivernano-wire, the first material layer 330 made of tungsten disulfide (WS₂)and the second material layer 340 made of tungsten diselenide (WSe₂)vertically overlap may be identical with a photoluminescence signal (PLsignal) based on the wavelength in the second region as a rightlongitudinal end of the nano-structure 310. This means that thewavelength multiplexing may be achieved when the first and secondmaterial layers 330 and 340 may vertically overlap with each other.

FIG. 4 is a conceptional view for illustrating a wavelength multiplexingdevice in accordance with one embodiment of the present disclosure.Referring to FIG. 4, a wavelength multiplexing device 4000 may include ametal nano-structure 410, a first material layer 430, a second materiallayer 440, and a third material layer 450.

Each of the first material layer 430, the second material layer 440 andthe third material layer 450 may be made of a semiconductor material inwhich excitons may be induced therein. The first material layer 430, thesecond material layer 440 and the third material layer 450 may behorizontally spaced from each other. Each of the first material layer430, the second material layer 440 and the third material layer 450 mayinclude at least one selected from a group consisting of a transitionmetal dichalcogenide-based compound, a chalcogenide-based semiconductorcompound, a phosphorus-containing chalcogenide-based semiconductorcompound, and a phosphorus-containing semiconductor compound. In oneexample, the first material layer 430 may be made of molybdenumdisulfide (MoS₂), the second material layer 440 may be made of tungstendiselenide (WSe₂), and the third material layer 450 may be made oftungsten disulfide (WS₂). However, the present disclosure may be limitedthereto. Each of the first material layer 430, the second material layer440 and the third material layer 450 may be in the form of a thin filmhaving an atomic layer thickness.

Each of the first material layer 430, the second material layer 440 andthe third material layer 450 may induce therein first, second, and thirdexcitons therein when the voltage is applied thereto. Each of theamounts of the first, second, and third excitons induced therein may beadjusted by the voltage applied thereto.

The metal nano-structure 410 may be disposed on the first material layer430, the second material layer 440 and the third material layer 450. Inone example, the metal nano-structure 410 may be embodied as silver (Ag)nano-wires. However, the present disclosure is not limited thereto.Various metals may be employed for the nano-wires. In one example, themetal nano-structure 410 may be embodied as metal nano-rods. The metalnano-structure 410 may extend across the first material layer 430 andthen the second material layer 440 and then the third material layer450. In other words, the metal nano-structure 410 may partially overlapthe first material layer 430 and then the second material layer 440 andthen the third material layer 450 respectively.

The light source 420 may emit laser light with a wavelength λ₀ which inturn, may be incident on a first region of the metal nano-structure 410wherein the first region may overlap the first material layer 430. Thelaser light may induce the first excitons in the first material layer430 and may generate surface plasmon polaritons in the first region.Then, the first excitons and surface plasmon polaritons may be coupledwith each other in the first region to form first coupled surfaceplasmon polaritons (SSP1) which in turn, may propagate along the surfaceof the metal nano-structure 410.

Then, the first coupled surface plasmon polaritons may be absorbed bythe second material layer 440 and, thus, the second excitons may beinduced in the second material layer 440. Then, the second excitons andfirst coupled surface plasmon polaritons may be coupled with each otherto form second coupled surface plasmon polaritons (SSP2) which in turn,may propagate along the surface of the metal nano-structure.

Subsequently, the second coupled surface plasmon polaritons may beabsorbed by the third material layer 450 and, thus, the third excitonsmay be induced in the third material layer 450. Then, the third excitonsand second coupled surface plasmon polaritons may be coupled with eachother to form third coupled surface plasmon polaritons (SSP3) which inturn, may propagate along the surface of the metal nano-structure.

In one example, each of the first excitons may have a first wavelengthλ₁, while each of the second excitons may have a second wavelength λ₂different from the first wavelength, while each of the third excitonsmay have a third wavelength λ₃ different from the first and secondwavelengths. In one example, the second wavelength may be larger thanthe first wavelength while the third wavelength may be larger than thesecond wavelength. Each of the first, second, and third wavelengths maybe determined by each of bandgaps of the first, second, and thirdmaterial layers 430, 440 and 450. Thus, Each of the first, second, andthird wavelengths may be adjusted by changing the type of the transitionmetal dichalcogenide-based compounds forming the first, second, andthird material layers 430, 440 and 450 respectively.

The third coupled surface plasmon polaritons may propagate along thesurface of the metal nano-structure 410 while different wavelengths (thefirst to third wavelengths) thereof are multiplexed. Thus, the thirdcoupled surface plasmon polaritons may be scattered on a longitudinalend of the metal nano-structure 410 to be decoupled into first lightwith the first wavelength, second light with the second wavelength andthird light with the third wavelength. Thus, the third coupled surfaceplasmon polaritons may be demultiplexed into the first light with thefirst wavelength, the second light with the second wavelength, and thethird light with the third wavelength. In this way, the first light withthe first wavelength, the second light with the second wavelength andthe third light with the third wavelength may be collected individually.The collection of the first to third wavelengths λ₁, λ₂, and λ₃ may beemployed for corresponding communications.

In accordance with the present disclosure, it is possible to generatethe multiplexed wavelength using the light source. The presentdisclosure can overcome the light diffraction limitation by using thesurface plasmon polaritons. The present disclosure has an effect ofbeing applicable to light communication.

Example for Production of Wavelength Multiplexing Device

Pieces of mono-molecule layers made of molybdenum disulfide (MoS₂),tungsten disulfide (WS₂) and tungsten diselenide (WSe₂) respectively aresynthesized by a vapor phase reaction method. The pieces of themono-molecule layers are transferred onto a silicon wafer having asilicon oxide thickness of 300 nm formed thereon. Then, isopropylalcohol solution containing dispersion of silver nano-wires, each wirehaving a diameter of 200 nm or less, is transferred onto the pieces ofthe mono-molecule layers and is dried under an atmospheric condition.

The electrical connections to the pieces of the mono-molecule layers arefabricated by metal evaporation of chrome/gold (thickness 10/50 nm) andelectron-beam lithography patterning method. A back gate bias (V_(G)) isapplied to the silicon wafer.

To protect the nanowires under the atmospheric condition, the nanowiressurfaces are coated with a protective layer made ofpoly(methylmethacrylate) 400 nm or less thick.

The above description is not to be taken in a limiting sense, but ismade merely for the purpose of describing the general principles ofexemplary embodiments, and many additional embodiments of thisdisclosure are possible. It is understood that no limitation of thescope of the disclosure is thereby intended. The scope of the disclosureshould be determined with reference to the Claims. Reference throughoutthis specification to “one embodiment,” “an embodiment,” or similarlanguage means that a particular feature, structure, or characteristicthat is described in connection with the embodiment is included in atleast one embodiment of the present disclosure. Thus, appearances of thephrases “in one embodiment,” “in an embodiment,” and similar languagethroughout this specification may, but do not necessarily, all refer tothe same embodiment.

What is claimed is:
 1. A wavelength multiplexing device comprising: afirst material layer made of a first semiconductor material; a secondmaterial layer made of a second semiconductor material, wherein thefirst material layer is spaced from the second material layer; anelongate metal nano-structure having first and second opposinglongitudinal ends, wherein the elongate metal nano-structure extendsacross and on the first and second material layers; a light sourceconfigured to irradiate light onto a first region of the metalnano-structure, wherein the first region overlaps the first materiallayer, wherein when the light is irradiated on the first region of themetal nano-structure, surface plasmon polaritons are generated on thefirst region of the metal nano-structure, and first excitons are inducedin the first material layer, wherein the surface plasmon polaritons andthe first excitons are coupled with each other to form first coupledsurface plasmon polaritons, wherein the first coupled surface plasmonpolaritons propagate along and on a surface of the metal nano-structure,wherein when the first coupled surface plasmon polaritons reach thesecond material layer, second excitons are induced in the secondmaterial layer, wherein the second excitons and the first coupledsurface plasmon polaritons are coupled with each other to form secondcoupled surface plasmon polaritons, and wherein the second coupledsurface plasmon polaritons propagate along and on a surface of the metalnano-structure.
 2. The device of claim 1, wherein each of the firstexcitons has a first wavelength, and wherein each of the second excitonshas a second wavelength different from the first wavelength.
 3. Thedevice of claim 2, wherein the second coupled surface plasmon polaritonsare decoupled at one of the first and second longitudinal ends of themetal nano-structure into first light with the first wavelength andsecond light with the second wavelength.
 4. The device of claim 1,further comprising a semiconductor substrate having an insulating filmformed thereon, wherein the first and second material layers aredisposed on the insulating film.
 5. The device of claim 4, wherein avoltage is applied to the substrate.
 6. The device of claim 1, whereineach of the first and second layers is electrically grounded.
 7. Thedevice of claim 5, wherein an amount of the induced first and/or secondexcitons is adjusted by the voltage applied to the substrate.
 8. Thedevice of claim 1, wherein each of the first and second material layeris in a form of a thin film having an atomic layer thickness.
 9. Thedevice of claim 1, wherein each of the first and second semiconductormaterial includes at least one selected from the group consisting of atransition metal dichalcogenide-based compound, a chalcogenide-basedsemiconductor compound, a phosphorus-containing chalcogenide-basedsemiconductor compound, and a phosphorus-containing semiconductorcompound.
 10. A wavelength multiplexing device comprising: a firstmaterial layer made of a first semiconductor material; a second materiallayer made of a second semiconductor material, wherein the firstmaterial layer is spaced from the second material layer; a thirdmaterial layer made of a third semiconductor material, wherein the thirdmaterial layer is spaced from the second material layer, and the secondmaterial layer is disposed between the first and third material layers;an elongate metal nano-structure having first and second opposinglongitudinal ends, wherein the elongate metal nano-structure extendsacross and on the first, second and third material layers; a lightsource configured to irradiate light onto a first region of the metalnano-structure, wherein the first region overlaps the first materiallayer, wherein when the light is irradiated on the first region of themetal nano-structure, surface plasmon polaritons are generated on thefirst region of the metal nano-structure, and first excitons are inducedin the first material layer, wherein the surface plasmon polaritons andthe first excitons are coupled with each other to form first coupledsurface plasmon polaritons, wherein the first coupled surface plasmonpolaritons propagate along and on a surface of the metal nano-structure,wherein when the first coupled surface plasmon polaritons reach thesecond material layer, second excitons are induced in the secondmaterial layer, wherein the second excitons and the first coupledsurface plasmon polaritons are coupled with each other to form secondcoupled surface plasmon polaritons, wherein the second coupled surfaceplasmon polaritons propagate along and on a surface of the metalnano-structure, wherein when the second coupled surface plasmonpolaritons reach the third material layer, third excitons are induced inthe third material layer, wherein the third excitons and the secondcoupled surface plasmon polaritons are coupled with each other to formthird coupled surface plasmon polaritons, wherein the third coupledsurface plasmon polaritons propagate along and on a surface of the metalnano-structure.
 11. The device of claim 10, wherein a voltage is appliedto each of the first, second, and third material layers.
 12. The deviceof claim 10, wherein each of the first excitons has a first wavelength,wherein each of the second excitons has a second wavelength differentfrom the first wavelength, wherein each of the third excitons has athird wavelength different from the first and second wavelengths. 13.The device of claim 11, wherein an amount of the induced first, secondand/or third excitons is adjusted by the voltage.
 14. The device ofclaim 10, wherein the metal nano-structure has a protective coatingformed on a surface thereof.